Would a fish in a sealed ball swim normally? This question led me to wonder whether swimming would be the same experience for a fish in a full, sealed ball as it is normally.
If the fish is about 7cm from the walls of the tank, a pressure wave can propagate from the fish to the wall and back in .0001 seconds, while the time scale on which a fish wiggles is tenths of a second.  So unlike the open ocean, the water surrounding the fish can all communicate with itself on the time scale that the fish wiggles, and unlike a normal fish tank, the water has nowhere to go and so can't change its shape.  
Would the fish notice any hydrodynamic effects in a full, sealed tank compared to normal swimming?
 A: Yes, the fish will swim normally.  The fish does not make itself move by radiating pressure waves to infinity, it creates and sheds small local vortices with its fins which move at a much lower speed. edit
A: It is not sound propagation but rather momentum diffusion that makes a fish swim. The rate at which momentum diffuses is determined by the kinematic viscosity, which for water is about $10^{-6} m^2/s$. 
It takes minutes for momentum to diffuse in water over distances of centimeters, while the time scale over which a fish wiggles is tenths of a second. So, during a wiggle the water surrounding the fish doesn't 'communicate' with any wall, and the fish doesn't notice any anomalous hydrodynamic effects. 
A: Yes the fish will swim normally.  Most people who have fish in an aquarium would agree.  Would those fish lose the ability to swim if I lowered plate glass onto the water surface to make a totally encapulated swimming space?  No.
Another way to look at it:  If you had a totally encased mixing bowl, which was totally filled with water, and manufactured so as to have the mixing blades (inside the bowl) driven by shafts which passed through hermetically sealed openings in the lid of the bowl to the electric blender motor.  When you turn the blender on, do the blades move?  you bethcha, they do.  So do fish fins.
A: When we compare an ocean/open water body to a sealed tank, there is an evident difference in volume and surface area. Therefore, the pressure that acts on the fish will be different since density of water will be different. Perhaps the fish might have to use its gills to form vortices to intensify from which the fins somehow harvest energy to move its fins and swim. 
